Acute Mountain Sickness

About Acute Mountain Sickness

Altitude Sickness, also known as AMS, is an illness that occurs at high altitudes, usually 2500 metres or more above sea level. It can affect anyone, whatever their age or fitness level, and you won’t know whether you’ll be affected until you’re at a high altitude – there’s no way of telling beforehand who will suffer and who won’t.

Some people are more prone to altitude sickness than others. In fact the reason so many Everest expeditions fail is AMS, which can affect the mental, emotional and physical performance of professional climbers so badly they can’t complete their goals.

About 50% of us will experience some form of AMS above 3500 metres, and in 5% of us it can be life-threatening.

Where Does Acute Mountain Sickness Occur?

AMS can occur anywhere in the world if you’re at a high altitude. Some of the most popular high altitude destinations for travellers are:

The Andes in South America, which include the Inca Trail in Peru and Quito in Ecuador

The Himalayas in Nepal and China, including the Everest Base Camp walk

There are also a number of airports where you land in a high altitude area, one 2000 metres or more above sea level. Flying straight into a high altitude environment gives people very little time to acclimatise, which can cause problems. These airports include:

If you travel to these airports you might experience mild AMS. If so, it helps to spend time acclimatising in the local area before travelling to a higher altitude. Slow and steady acclimatisation works best.

Signs and Symptoms of Acute Mountain Sickness

Above 2500 meters, many people will experience mild AMS. The signs and symptoms differ from person to person but include dizziness, a headache, feeling sick and vomiting, a puffy face and limbs, fatigue and irritability, difficulty sleeping and a loss of balance.

Mild AMS is uncomfortable but usually passes in a few days as long as you don’t climb any higher. But at the same time mild AMS is a warning sign, hinting that you might be vulnerable to severe AMS if you ignore the signs and keep ascending.

At more than 4000 metres above sea level, around 5% of people will develop a more serious and severe form of AMS. It can develop slowly, following on from mild AMS or coming on very quickly. Symptoms include fluid on the lungs and brain. Both are very serious and can be life-threatening. If you experience these symptoms it’s vital to find medical assistance and descend immediately.

How to Prevent Acute Mountain Sickness

The best way to prevent altitude sickness is to climb slowly and steadily, avoiding rapid increases in ascent in short periods of time. Sensible advice for acclimatisation includes:

Resting for a day or two for every 1000 metres you’ve climbed

Sleeping at a lower altitude than the highest point you’ve reached that day

Once you’re over 3000 metres up, do not increase your sleeping altitude by more than 300 metres a day

If you start to feel ill or show any signs of AMS, do not climb any higher until you are feeling better

If your symptoms do not improve or they get worse fast, get yourself down to a lower altitude immediately, no delays

Acute Mountain Sickness Advice

Keep hydrated by drinking between 4 and 5 litres of water per day. The atmosphere at high altitude is thin and dry and you will lose a lot of fluid through sweating and breathing

Make sure you keep your energy levels up. Your body will be under increased stress pumping extra oxygen as well as using extra energy to climb and carry heavy kit,

Never walk alone – make sure you have a walking or climbing partner, since you may not be able to recognise the symptoms of AMS in yourself

Make sure you know where the nearest healthcare facilities are

Avoid alcohol

Treatment of Acute Mountain Sickness

The best way to treat AMS is to descend as quickly and safely as possible. For severe AMS, medical intervention may be required.

Acetazolamide (Diamox)

Acetazolamide or Diamox is a drug which can help prevent and treat mild AMS. But Diamox is not a replacement for acclimatisation. If you are using Dixmox and ascend too fast, you’re still at risk of getting AMS.

Need to know more? Our nurse prescriber will provide extra information about the risks and benefits of Diamox.